Internal combustion engines may include at least one cylinder head connected to an engine block to form one or more cylinders. To hold the pistons and/or cylinder liners, the cylinder block which may form a crankcase, has cylinders bores which correspond to the number of cylinders in the engine. The pistons may be guided in the cylinder liners in an axially movable fashion and, together with the cylinder liners and the cylinder head, form the combustion chambers of the internal combustion engine.
Internal combustion engines may be boosted to increase the power output of the engine. Providing boost to engines involves compression intake air delivered to the combustion chambers. Devices used to provide boost include turbochargers and superchargers. Superchargers may include compressors which are mechanically driven via the transmission while turbochargers may use exhaust gas to drive a turbine which in turn is rotationally coupled to a compressor. Specifically, in a turbocharger the compressor and turbine may be arranged on the same shaft. Hot exhaust-gas flow may be supplied to the turbine, expanding in said turbine with a release of energy and setting the shaft, which is mounted in a bearing housing, into rotation. The energy supplied by the exhaust-gas flow to the turbine and ultimately to the shaft is used for driving the compressor, which is likewise arranged on the shaft. The compressor conveys and compresses the charge air supplied thereto. As a result, boosting of the engine is achieved.
One of the benefits of an exhaust-gas turbocharger, for example in relation to a mechanical charger (e.g., supercharger), is that no mechanical connection for transmitting power is needed between the compressor and internal combustion engine. In contrast, mechanical chargers, such as superchargers, extract the energy for driving the compressor from the crankshaft of the internal combustion engine, thereby reducing the power output of the engine and consequently adversely affecting engine efficiency. In contrast, turbochargers utilize the exhaust-gas energy of the hot exhaust gases which are directed to the surrounding environment.
Boosted internal combustion engines may be equipped with a charge-air cooling arrangement configured to cool the compressed combustion air before entering the cylinders. As a result, the density of the supplied charge air is further increased. In this way, the cooling likewise contributes increasing the density of the air delivered to the cylinders. In other words, the volumetric efficiency of the combustion chambers is increased.
Boosting engines, and in particular turbocharging engines, enables the power of the engine to be increased while maintaining an unchanged swept volume, or enables a reduction in swept volume while maintaining the same power output. Therefore, Boosting engines provided an increase in the volumetric power output and/or provide an increased power-to-weight ratio. For the same vehicle boundary conditions, it is thus possible to shift the load collective toward higher loads at which the specific fuel consumption is lower. This is also referred to as downsizing.
However, problems are encountered in the configuration of the exhaust-gas turbocharging, where it is desirable to achieve a performance increase over a wide range of rotational speed ranges. In some engines, a severe torque drop is commonly observed if the rotational speed drops below a certain rotational speed. Further in some engines improvements in torque characteristics of the engine may be desired. To achieve the enhanced torque characteristics attempts have been made to reduce the size of the cross-section of the turbine and simultaneous exhaust-gas blow-off. If the exhaust-gas mass flow exceeds a threshold value, a part of the exhaust-gas flow is conducted, within the course of the exhaust-gas blow-off, via a bypass line past the “waste-gate turbine”. However, said approach has some downsides at relatively high rotational speeds.
Other attempts have been made to improve the torque characteristics of the engine via a plurality of turbochargers provided in a series and/or parallel arrangement. However, boosting engines may increase the thermal loading on the engine caused by the increasing the pressure of the intake air when compared naturally aspirated engines. As a result, increased demands are placed on the cooling arrangement in the engine. To keep the thermal loading within limits, boosted internal combustion engines may be equipped with a cooling arrangement, also referred to as an engine cooling arrangement. It is possible for the cooling arrangement to take the form of an air-cooling arrangement or a liquid-cooling arrangement. Since significantly greater amounts of heat may be dissipated by means of a liquid-cooling arrangement, a liquid-cooling arrangement may be used in many engines.
In some liquid-cooling arrangements, a cylinder block coolant jacket and a cylinder head coolant jacket may be provided. The coolant jackets may include coolant passages traversing the cylinder block and/or cylinder head. Adding the coolant passages increases the complexity of the structure. Additionally, the coolant passages may decrease the strength of the cylinder head or cylinder block which are mechanically and thermally loaded. Furthermore, in liquid-cooling arrangements heat is dissipated to the coolant, generally water provided with additives, in the interior of the cylinder head or cylinder block. In this case, the coolant is conveyed, such that it circulates, by a pump which may be arranged in the cooling circuit and which may be mechanically driven by a traction mechanism drive. The heat dissipated to the coolant is thereby discharged from the interior of the cylinder head or cylinder block and is extracted from the coolant again in a heat exchanger. A ventilation vessel may be provided in the cooling circuit. The ventilation vessel may ventilate the coolant or the circuit. In other words, vapor may be removed from the coolant in the circuit and flowed to the ventilation vessel.
Like the internal combustion engine itself, turbines in exhaust-gas turbochargers may have increased thermal loadings. Therefore, the turbine housing in some prior art turbochargers may be produced from heat-resistant material which may contain nickel and/or may be equipped with a liquid-cooling arrangement. EP 1 384 857 A2 and German laid-open specification DE 10 2008 011 257 A1 describe liquid-cooled turbines and turbine housings.
The hot exhaust gas of the turbocharged internal combustion engines may also lead to high thermal loading of the bearing housing and consequently on the bearing of the turbocharger shaft. Furthermore, a large amount of heat may be transferred to the oil provided to the bearing for lubrication. On account of the high rotational speed of the turbocharger shaft, the bearing may be formed as a plain bearing rather than a rolling bearing. As a result, of the relative movement between the shaft and the bearing housing, a hydrodynamic lubricating film, which is capable of supporting loads, forms between the shaft and the bearing bore. Increasing the temperature of the oil decreases the oil's viscosity, thereby degrading the friction characteristics of the oil. Additionally, increasing the temperature of the oil accelerates the oil's aging, thereby degrading the oil's lubrication properties. Both of these phenomena shorten the service interval for oil changes and can pose a risk to the functional capability of the bearing, wherein even irreversible destruction of the bearing and therefore of the turbocharger is possible.
Therefore, the bearing housing of a turbocharger of an internal combustion engine may be equipped with a liquid cooling arrangement. Here, a distinction must be made between the liquid-cooling arrangement of the bearing housing and the abovementioned liquid-cooling arrangement of the turbine housing. Nevertheless, the two liquid-cooling arrangements may be connected to one another, optionally only intermittently, that is to say fluidly communicate with one another.
In contrast to the engine cooling or cooling of the turbine housing, it may be desirable to maintain the cooling of the bearing housing when the vehicle has been shut down, that is to say the internal combustion engine has been switched off, at least for a certain period of time after the internal combustion engine has been switched off, in order to reduce the likelihood irreversible damage to the turbine housing as a result of thermal overloading. This may be achieved by an additional, electrically operated pump which is powered, for example, by the on-board battery, which pump conveys coolant via a connecting coolant line through the bearing housing when the internal combustion engine has been switched off and therefore provides cooling of the bearing housing and of the bearing even when the internal combustion engine is not in operation. The provision of an additional pump is, however, a comparatively costly measure.
Some engines may not include an additional pump. In this case, the connecting coolant line, which leads from the cooling circuit of the engine-cooling arrangement through the bearing housing of the exhaust-gas turbocharger as far as the ventilation vessel, is designed as a rising line, at least upstream of the bearing housing. The conveying of the coolant when the internal combustion engine is switched off may be achieved by what is referred to as the thermosiphon effect, which is essentially based on two mechanisms.
Owing to the introduction of heat, which continues even when the internal combustion engine is switched off, from the heated bearing housing into the coolant situated in the connecting coolant line, the coolant temperature increases, as a result of which the density of the coolant decreases and the volume taken up by the coolant increases. Superheating of the coolant may furthermore lead to a partial evaporation of coolant, and therefore coolant passes into the gaseous phase. In both cases, the coolant expands and takes up a larger volume, as a result of which ultimately further coolant is displaced, that is to say conveyed, in the direction of the ventilation vessel. Coolant is supplied as a result of the negative pressure which arises.
However, the Inventors have recognized several problems with using a thermosiphon to convey coolant to a bearing housing. Due to the constricted space conditions in the engine compartment of a vehicle, it may not be possible to form the connecting coolant line as a rising line upstream of the bearing housing or to realize the difference, which is needed for the thermosiphon effect, in the vertical height between the bearing housing and ventilation vessel. The reasons are as follows. It may be desirable in the use of an exhaust-gas turbocharger to arrange the turbine of the at least one charger adjacent to the outlet of the internal combustion engine, that is to say the outlet openings of the cylinders, in order to be able to use the enthalpy of the hot exhaust gases, the enthalpy being decisively determined by the exhaust-gas pressure and the exhaust-gas temperature, and to ensure a rapid response behavior of the turbocharger. For the reasons mentioned above, the turbine of the exhaust-gas turbocharger may be arranged directly on the cylinder head and therefore in a position which has a comparatively high vertical height, that is to say in the installed position in an internal combustion engine is positioned at a high point with regard to the other components and assemblies.
This installed position of the turbine or of the bearing housing makes it difficult to design the connecting coolant line upstream of the bearing housing as a rising line in which the vertical height continuously increases. This is because the ventilation vessel cannot be arranged at an arbitrary height above the bearing housing. In particular, for safety reasons, that is to say because of the demands imposed on the crash performance of the vehicle, the components and assemblies installed in the engine compartment may be maintained at a predetermined distance from the engine hood. The maintaining of a prescribed safety distance from the engine hood inevitably leads to an only small difference in height between the bearing housing and ventilation vessel, the lack of a difference in height or, in a particular case, even to a negative difference in height, in which the bearing housing is at a greater vertical height than the ventilation vessel.
The packaging constraints previously mentioned make it difficult to use a thermosiphon to cool the bearing housing to a desired level. Specifically, when the ventilation vessel is positioned in an unfavorable position the resistance against the coolant conveyed from the bearing housing is increased. The result is a longer residence period in the bearing housing, wherein the coolant may be greatly superheated and the pressure may rise sharply, even in the connecting coolant line upstream of the bearing housing.
As a result, superheated coolant vapor of relatively high pressure, in particular coolant vapor, may pass via the connecting coolant line into the ventilation vessel. This may firstly lead to thermal overloading, damage or destruction of the vessel, which may be produced from plastic. Secondly, the increased vessel pressure may lead to a pressure control valve arranged on the vessel opening in an uncontrolled manner and releasing vaporous coolant into the surroundings. This may cause an undesirable production of noise, in particular a whistling. The vessel is generally provided with a cover which closes a vessel opening, which serves for the pouring in of coolant, and frequently also accommodates the pressure control valve. The greatly superheated coolant may also act on the cover and/or the cover seal and lead to the cover sticking.
Furthermore, the above-described pressure and temperature conditions may lead to a pulsating conveying of the coolant, in which the coolant is introduced into the ventilation vessel via the connecting coolant line in surges. This results in frothing and enrichment of the coolant with air. These effects act counter to the actual purpose of the ventilation vessel, namely of degassing, that is to say of ventilating, the coolant.
To solve at least some of the aforementioned problems a thermosiphon system in an engine is provided. The thermosiphon system includes a coolant channel traversing a bearing housing, the bearing housing included in a bearing coupled to a shaft mechanically coupled to a turbine and a compressor in a turbocharger, a ventilation vessel in fluidic communication with at least one coolant passage traversing at least one of a cylinder head and a cylinder block in the engine, the at least one coolant passage included in a cooling circuit, and a thermosiphon coolant line having an inlet in fluidic communication with an outlet of the coolant channel and an inlet of the ventilation vessel, the inlet positioned vertically below an interface between liquid and vapor coolant in the ventilation vessel.
When the coolant in the thermosiphon coolant line is introduced into the ventilation vessel into the liquid coolant housed within the vessel, the temperature of the heated coolant is reduced. As a result, the likelihood of degradation of the housing of the ventilation vessel as well as other components in the ventilation vessel, such as a purge valve which may be positioned near the top of the vessel, is reduced. In this way, the thermosiphon system enables heat to be removed from the turbocharger bearing while at the same time reducing the likelihood of ventilation vessel degradation from heated coolant from the thermosiphon coolant line.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.
The figures are described in greater detail below.